I have a 29/30 gallon and I keep 1 german blue ram and 1 Apistogramma Agazzi in it in addition to a few other fish.
If you do more than one (pairs or more) I would stick to one species, and try to get only 1 male to 2 or 3 females (for the apisto).
instead of getting a few of one kind, I have the two different species afore mentioned.
Apisto is almost 2 inches (max out @ 3") and the ram is maybe an inch and a half (max out @~2.5") They are not yet full grown, but so far they seem to do just fine together. The Apisto is the dominant of the two, and he sticks down low, while the ram seems fine hangin in the middle or gowin down low.
I did 1 each of the different species because multiple males of the same species will not have enough room in a 29. The interspecies agression, although still there, seems tolerable split between the GBR and the Apisto Agazzi.
Good luck!